National Electrical Installation Standards

Standards as High as Your Own

Monday, September 14, 2020


Good morning, thanks for keeping up code question of the day. The local inspector stated we need to keep the smoke detectors a minimum of 3' away from return air in residential work. I understand being 3' away from supply air but I would think it would only be beneficial as smoke would be pulled to a supply air return.

Bill McDermott



Hi Bill,

Thanks for the question. The NEC does not cover required or recommended locations for single station smoke alarms or smoke detectors installed on a fire alarm system. The NEC contain installation rules for the wiring of such equipment. See NEC Article 760. NFPA 72 recommends installing smoke detectors a minimum of 3 feet from any air supply or return air grill. They may need to be installed farther away when air velocity is higher than normal. Near the return grills, smoke detectors may not respond as quickly as they should because of air turbulence near the grill, which is caused by air from the room being forced to enter a relatively small opening.

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